The present invention relates to an actuator and in particular, but not exclusively, to a jam-tolerant electromechanical actuator for moving an aircraft component.
Actuators may be used to cause movement of aircraft components such as the landing gear of an aircraft, for example steering the nose landing gear. Such actuators should of course be of high integrity and should have a very low risk of failure. For example, it is important for actuators to have at least two modes of operation so that there is for example a secondary, or emergency, mode of operation that facilitates movement of the aircraft component in the event of a loss of, or failure in, the normal mode of operation. Such a secondary, or emergency, mode of operation may provide for active movement of the aircraft component or may simply allow for the aircraft component to be moveable despite being connected to the actuator (in the context of a landing gear steering actuator, the secondary, or emergency, mode of operation may consist of allowing free-castoring of the landing gear).
There are two main types of electromechanical actuators, namely linear actuators and rotary actuators. Linear actuators typically feature an electric motor coupled to a reduction gear-box connected to a roller or ball screw. The high-speed/low-torque rotating motion of the electric motor is converted into low-speed/high-thrust linear motion. Rotary actuators also typically feature an electric motor connected to a reduction gear-box, in this case the high-speed/low-torque rotating motion of the electric motor is converted into low-speed/high torque rotary motion. Depending on the application either linear or rotary motion may be needed. For example, the extension/retraction system of an aircraft landing gear may require a linear actuator, whereas the operation of doors or the nose wheel steering of an aircraft may require a rotary actuator.